Homemade tartar sauce will keep, tightly covered, for up to a week when stored in the refrigerator.
Homemade Tartar Sauce
½ cup mayonnaise
1 gherkin pickle
1 tablespoon capers
1 tablespoon white wine vinegar
1 teaspoon coarse-grained mustard
Pinch kosher salt
Pinch freshly ground black pepper
Put all the ingredients in a food processor or mini chopper fitted with a steel blade, and pulse until the pickles are finely chopped and all the ingredients are mixed but not puréed. Cover and store in the refrigerator for at least 30 minutes before serving.